Brake shoe composition of phenol-form-aldehyde resin, an unvulcanized rubber, asbestos fiber, iron chips, and carbon black and method of making same



United States Patent Ofilice BRAKE SHOE COMPOSITION OF PHENOL-FORM ALDEHYDE RESIN, AN UNVULCANIZED RUB BER, ASBESTOS FIBER, IRON CHIPS, AND CAR- BON BLACK AND METHOD OF MAKING SAME John B. Evans, Irwin, Pa., assignor to Westinghouse Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvania No Drawing. Application February 25, 1957 Serial No. 642,314

5 Claims. (Cl. 260-48) my application, 7 and abandoned following the filing of the instant application.

It is desirable that brake shoes used on railway vehicles have relatively long service life and that they do of braking surface of the shoes and wheels as Well as under other varying conditions of operation, such as on dry rails and rails which are wet. Up to the present time, so far as is known, no material has ever been devised which provides all of these desirable characteristics in the same shoe. 7

Brake shoes made of cast ure the above-mentioned various desirable characteristics,

far as is known without success, to develop materials which, either in themselves or in various combinations with cast iron, would provide more nearly than do cast iron shoes in common usage, the various desirable characteristics above-mentioned.

It is accordingly the principal object of the present invention to provide a composition material particularly adapted for use as brake shoes on railway vehicles which more nearly attains all the above-mentioned desirable characteristics in the same shoe than, so far as the applicant is aware, has ever before been attained in any one shoe.

I have discovered that a certain composition material made of constituent elements in certain proportions and by the method to be described herein provides better and more stable frictional characteristics for brake shoes under the various conditions such as different wheel speeds, operating temperatures, and other variable conditions, and at the same time, provides longer wear life 2,910,449 Patented Oct. 27, 1959 for the shoes and less abrading efiect on car Wheels than any material, heretofore have been made,

The ingredients used in making my improved composition material for brake shoes and their constituent percentage ranges by weight are as follows:

Ingredients Unvulcanized powdered rubber known, of which brake shoes Percent by weight (natural or synthetic) 4 to 10 Phenol-formaldehyde resin 8 to 15 Asbestos fiber (short) 12 to 20 Carbon Black 0 to 10 Cast iron chips (of sizes that will pass through a A" mesh screen and be retained on a hi mesh screen) 60 to For example, I find that a composition material without rubber-vulcanizing ingredients composed of 4 percent unvulcanized powdered rubber either natural rubber and/ or a synthetic butadiene acrylonitrile rubber such as Hycar OR15, 8 percent phenol-formaldehyde resins such as Durez Companys 12687 resin or Bakelite phenolic plastic, a product of the Bakelite Company, 13 percent asbestos fiber, and 75 percent cast iron chips within the In carrying out the invention in brake shoes possessing the desired properties and characteristics, I find that lowed: accurately proportioning the above ingredients according to the above a degree suificient to soften there'sin placing the preformed and preheated mixture in a hot brake mold and again applying mixture prior to subsequent application of pressure while in the mold, so that such application of pressure will be capable of effecting maxiresins in such mixture. For example, it has been found that for a five pound mixture of ingredients suitably formed in a container, uniform softening without hardening of the resin was attained by preheating such preformed mixture in an air circulating oven at 200 to 225 Fahrenheit for about thirty minutes, or, by preheating such preformed mixture in a dielectric heater of the electronic heat generator type (such as manufactured by W. T. La Rose and Associates under the trade name Thermal) for a much lesser period of time, such as ten minutes, at temperatures ranging from 200 to 300 F.; the oven heating method requiring considerably more time to allow for penetration of heat to the interior of the preformed mass prevent hardening of the resin in the outer surface of such mass during the relatively long period of heat application; while the dielectric heating method, in heating simultaneously throughout such mass, speeds up the resin softening process and thereby renders the preheat temperature of the mixture less critical and much less dependent on the mass of the mixture.

The temperature of the hot mold, in which the suitable quantity of preheated and preformed materials is placed, is preferably between 300 F. to 340 F. to hasten the hardening of such materials while under subjection to compaction pressure. At such temperature and at a compaction pressure of 3500 lbs. per square inch, the hardening may be completed in a period of about forty minutes, after which the pressure is relieved and the completed shoe is removed from the mold and allowed to cool.

It is desired to point out that, while some of the aforementioned ingredients used in my improved brake shoe have heretofore been used in various different compositions for brake shoes, nevertheless, so far as I am aware, my employment of all of these elements together and in the proportions herein specified and molding them together under conditions of heat and pressure in the absence of rubber-vulcanizing ingredients is believed to be novel and, as demonstrated by actual tests, provides a very superior brake shoe combining the desirable characteristics of a relatively high coefiicient of friction, a low rate of brake shoe wear, and a low rate of wear of the conventional railway car wheel braked by such a brake shoe.

Having now described the invention, what I claim as new and desire to secure by Letters Patent is;

and requiring a low temperature to mixture consisting of, by weight, 4 to 1. A method of making a rial having characteristics m for use as a frictio method comprises composition friction mateaking it especially suitable material for a brake shoe, which molding under heat and pressure a 10% unvulcanized butadiene-acrylonitrile copolymer synthetic rubber, 8 to 15% phenol-formaldehyde resin,

cast iron chips, and up fiber, to black.

2. A method rial having characteristics for use as a friction materi making it esp which method comprises molding under sure a mixture consisting of, by weight,

20% asbestos to 5% carbon of making a composition friction mateecially suitable al for a railway brake shoe,

heat and presabout 4% unvulcanized butadiene-acrylonitrile copolymer synthetic rubber, about 8% phenol-formaldehyde re asbestos fiber, about 75% mainder carbon black.

sin, about 13% cast iron chips, and the re- 3. A method of making a composition friction material having characteristics making it esp sure a mixture consisting of, by weight,

ecially suitable for use as a friction material for a railway brake shoe,

heat and presabout 5% unvulcanized butadiene-acrylonitrile copolymer synthetic phenol-formaldehyde resin, about about 5% carbon black, and about rubber, about 10% 14% asbestos fiber, 66% cast iron chips 4. The method define ized in that the cast iron c pass through a A" mesh screen.

mesh screen and be d in claim 3, further characterhips are of such sizes as will retained on a 5. A molded product made according to the method defined in claim 1.

References Cited in the file of this patent UNITED STATES PATENTS Butterich De Gauge Shepard et a1.

Cunnen et al.:

Compounds, Journ pages 472-476 Rubber,

al Am. Chem. Soc,

Aug. 13, 1940 Aug. 10, 1954 Nov. 19, 1957 Polyisoprenes and Allied October 1943, 

1. A METHOD OF MAKING A COMPOSITION FRICTION MATERIAL HAVING CHARACTERISTICS MAKING IT ESPECIALLY SUITABLE FOR USE AS A FRICTION MATERIAL FOR A BRAKE SHOE, WHICH METHOD COMPRISES MOLDING UNDER HEAT AND PRESSURE A MIXTURE CONSISTING OF, BY WEIGHT, 4 TO 10% UNVULCANIZED BUTADIENE-ACRYLONITRILE COPOLYMER SYNTHETIC RUBBER, 8 TO 15% PHENOL-FORMALDEHYDE RESIN 12 TO 20% ASBESTOS FIBER. 60 TO 75% CAST IRON CHIPS AND UP TO 5% CARBON BLACK. 